Conversion of hydrocarbons



Dec..26, 1939;

R. F. TROW CONVERSION OF HYDRO'CARBONS4 Filed June 30, 1958 Sn INVENTOR //cf/A A'. 750W @man ATTORNEY Patented Dec. 26, 1939 rATENT OFFICE.

2,185,162 vCGNVERSION OF HYDROCARBONS `Richard vF. Trow, Tuckahoe, yN.r Y., assigner to The Texas Company, New York N. Y., `arcorporation of .Delaware y Application 'June so, 193s, serial No. 216,650 l Claims. (ci. 19e- 49) This invention relates to a process for the conversion 'of hydrocarbon oils to ygasoline of high vanti-knock value.

vIt 'iis yan object of the invention to provide a 5 process for Aeffecting ycracking of a relatively clean distillate oil under elevated conditions of temperature 'and pressure to effect conversion thereof to -fgasoline constituents of high antilcn'ock value and -simultaneously effecting the viscosity breaking of a `heavy voil in a manner whereby such viscosity Ebreaking assists in pre'- venting excessive coke deposition in the cracking of the distillate oil,feffects intermediate removal -of residual Aconstituents formed in the cracking of vthe distillate oil and effects `intermediate addition of preheated cracking stock to the distillate oil undergoing/cracking. ,'It is another object ofthe invention to provide a process of the vabove I`nature Awhich is cyclic 'in '20 operation landinvolves such -no'velvoperating improvements as will be v'rfound to pertain thereto from ythe -following description.

According to the present invention aclean distillate oil such as fa gas oil "issubjec'ted to crack'- ing fby ithepassage thereof as a stream through an elongated heating zone of Jrestricted cross section such' as a heated pipe coil, under elevated r conditions of temperature and pressure. After 4su'bstznitial cracking hasbeeneffected the stre-am of foil undergoing conversion is comming'led with a hydrocarbon voil having a higher boiling range than the said gas oil. This lheavy oil maybe a distillate koilfsuoh asa heavy gas oiljor maybe a' residual /oil such as topped or reduced crude. Theresultingmix'ture ismaintained under cracking conditions of temperature and Ypressure for a time suiiicient to effect viscosity breaking of the heavy oil, and the resulting products are separated fby passage yof the 'stream through a :zone 40 of enlarged -cross section,'at a velocityA substantially 'lo-wer than 'the velocity of "the stream in .passing through the pipe coiLinto a vapor fraction whichlincludes constituents "boiling above the gasoline 'boiling range and'fa liquid residue fraction. 'The vapor and liquid Acomponents of the stream are separately withdrawn from the zone of enlarged cross section, vwhich may be a separator connected tothepipe coil, andthe vapor componentris'passed as a streamthrough a'second pipe coilwh'erein itis .subjected to further cracking under elevated conditions yof temperature andv pressure. The admixture of lthe heavy oil with the stream :may be effected by introducing the .heavy oil into `theilrs-t pipecoil at a plurality of points .after which, `after :a suitable/interval,

lnaces arel the mixed stream maybe passed through the separator to effect the desired separation lof vapors and liquid residue; lor the heavy 'oil may be admixed with the stream undergoing cracking inA the separator whereby the desired viscosity breakingis effected in the separator. lThe volatilelproducts of the viscosity-breaking operation andV of the cracking of the gas oil are withdrawn from the separator Ias a vaporous stream and the residue from both crackingoperat'ions, including residual constituents introducedr into theseparator with the heavy oil, isY withdrawn therefrom separately. i

The pressure maintained 'in the separator may be substantially the same as or lower than that maintained yin the rst pipe coil, and the pressure maintained in Vthe, second pipe coil may be sub'- stantially the same or lower than thaty main.- tainedin the separator. Peferably', unnecessary reduction of pressure is avoided.

y The accompanying drawing is a diagrammatic viewin elevation of apparatus suitable for carrying out the process ofthe present invention. The invention will be vfurther described in detail by reference to the drawing. It will vbe understood, however, Vthatfthe drawing and `accompanying specic ldescription are merely illustrative of the inventionwhich'is capable of other'modiiications and embodiments than those illustrated and described.

In the drawing the cracking vof the distillate oil is effected 'in heater -I 'which' is provided with a cracking coil 2 divided 'into two sections, 2a and 2b, which are connected through intermediate separator 3. The drawing 'illustrates dia grammatically a furnace of the type wherein a pipe coil Ais arranged in a plurality of sections about the ywall of a furnace chamber which is circular 'in Ihorizontal cross section. 'Such' 'furo'rdinarily centrally fired whereby all parts of the coil 'thus arranged are equidistant from` the `zone of combustion or source of radiant heat. It is to be understood, however, that the two elongated cracking zones of restricted cross section employed in 'the present 'invention may be embodied 'by a pair o'f coils located in different parts of any conventional type `cracking furnace; or :they may be similar ordifferent 'coils located in separate furnaces. v"Forsimplicity-of illustration, however, a furnace vof the first-mentioned type is illustrated.

in addition to the furnace and intermediate separator the. apparatus lis provided with a. nal .separator 4, fractionator 5, .receiver 5 andstabilizer 66. Suitable pipe'.connectionsnare provided as shown for effecting transfer of the materials under treatment to and from the various treat'- ing` zones.

In the operation of the process as illustrated in the drawing the clean distillate oil, which may be a gas oil, is introduced into section 2a of pipe coil 2 through line I0 which is provided with a pump II for maintaining the desired pressure ,in the pipe coil 2. charged may consist entirely of fresh feed introduced from an external source clude recycle stock. In section 2a For example, in section 2a' of the pipe coil the stream passing therethrough may be heated to a temperature of the order of 900;F.l 000 1'. under a pressure of 20D-600 pounds per squarev inch.

According to one embodiment of the invention4 a heavy oil, which may be a-residual oil suchas reduced crude, is introducedinto section 2d of the pipe coil at an intermediate point thereof through line I2 which is provided with a pump I3. This heavy oil is suitably preheated prior to introduction into section 2a of the pipe coil and, for example, in thecas'e of reduced crudegmay be preheated to a temperature of 500 F.g700 F. It may be advantageous to heat the heavy oil to higher temperatures, for example, temperatures as high-as 825 F. to effect cracking prior to introduction linto coil 2a. The-temperature of the heavy oil thus introducedl vand the ratio of heavy oil to clean distillate undergoing cracking are regulated to produce the desired temperature conditions in Vthe remaining portion-of section 2a of the pipe coil-2. This temperature-ispreferably regulated to effectviscosityl brealdng of the heavy oil thus introduced with additional cracking of the clean distillate, as desired. The point of introductionof the heavyoil betweenthe entrance and exit of sectionv Zavof the pipefcoil v2 is chosen with respect to the degree of `cracking being eiected on the` clean distillate oil in the first part of sectionZa of `the pipe coil and the temperature to which the heavy-4 oil ispreheated whereby the heavy oil is admixedwith the stream undergoing crackingbefore excessive cokeformation occurs. 'I'he resulting mixture is thereafter withdrawn from section 2d through line I4, before 'excessive cracking of the tarry constituents of the mixture is effected, and lintroduced into intermediate separator 3 -wherein separation of vapors' and liquid residue is effected. -Intermediate separator 3 preferably' is maintained without reduction in temperature substantially below the cracking temperature. Suitable insulation may be provided for this purpose. Preferably also no unnecessary reduction in pressure is permitted in the passageof the cracked products from section 2a of the pipe coil to separator 3 although if desired' positive reductionin pressure may be effected by means -of valve I5 in lineI.

In separator 3 conditions 4of temperature'and pressure are maintained to eiTect separation only of relatively4 high boiling residual constituents and the passage overhead 'of a vapor fraction whichl v`contains substantially all constituents suitable for further cracking treatment.' The liquid residueseparated in separator 3 'iswvith-` drawn therefrom through line I6 provided with pressurecont'rolvalve '49 through which it may be passed lto a vacuum tower50 wherein a clean distillate such as a heavy'gaspil isf separated The gas oil thus` or may inlof the pipe coil the gas oil passed therethroughnis heated; under appropriate conditions of temperature and, pressure to effect substantial cracking thereof.

in separator 54 is withdrawn therefrom through r`4line 51 which is provided with pump 58 and connects withfline '38 whereby the gas oil thus separated is introduced into the upper portionv of separator I and reprocessed. In vorder to .permit proper scrubbing of the v'vapors in separator 3 it is desirable to cool vpart ofthe residue therefrom and reiiux the same over baflies in the top of separator 3. To this end a portion of the residual oil withdrawn from separator 3 through line I B may be diverted therefrom through line 'I5 which is provided-witha cooler I6, a pump 11 and connects' with ;lin e;| 9 whereby a portion of the residual oil is cooled and introduced into the upper portion of .separator 3. j

The vapor fraction separated in separator 3 is withdrawn therefrom through line I1 which connects with the inlet of sectontZb of pipe coil 2. This mixture of cracked productswithin and above the gasoline boiling range,-i n clud ing uncracked gas oil introduced throughv line I 0, distillate from the heavy oil introduced through line I2 and products `ofA the viscosity breaking of the heavy oil, is subjected -insection 2b to suitable conditions of temperature and pressure Vtoeifect conversion thereof to gasoline constituents of high anti-knock value. Preferably the pressure is not unnecessarily lower than that lexisting in separator 3; For example, the vapors passing through section 2b may be heated to a temperature of the order of 900 F.-1'000 F. under a pressure of 200-600 pounds per square inch. If desired, however, any suitable reduction inpressure may be effected between sepa rator 3 and section 2b of thepipe coil by means ofvalvelinlinel'l. 1- L According to another modication of the invention the products of cracking" of the distillate oil in section 2a of thepipe coil may be withdrawn therefrom through line I4V prior to admixture therewith of any heavy oiland priorto excessive coke formation; The products of conversion are introduced into separator 3 through, line I4 as describedv and therein are'contacted .v with a heavy oil introduced into separator 3 through line I 9 provided with pumpv 20. This heavy oil, `which may be a topped or reduced crude or heavy gas oil, is preferably preheated, for example to a cracking temperature: In separator 3 the products of crackingintroduced through line I4 and the heavy oil introduced through line I9 are intimately adm ixed whereby cracking and viscositybreaking of the heavy oil are effected togetherwith simultaneous separation of the products of thecracking operations and the distillation of the heavy oil into a vvapor The stream undergoing conversion is with drawn from section 2b ofthe pipe coil 2 through 'fraction and a liquidv residue. The Vresidue v to a nal separator 4. If desi-redl the products of cracking may be cooled by suitable means prior to introduction into separator 4, and any desired reduction in pressure may be effected by means of valve 22 located in line 2l.

In separator 4 conditions of temperature and pressure are maintained to effect separation of a heavy residue which is Withdrawn through line 23 and the passage overhead of a vapor fraction including constituents suitable for recycling to the entrance of pipe coil 2 through line 24 which connects the upper portion of separator 4 with fractionator 5. A portion of the residual oil withdrawn through line 23 may be diverted through liney 45, cooled by passage through cooler 46,k and admixed with the cracked products in line 2l, a pump 41 being provided in line 45. Fractionator 5 is operated under conditions of temperature and pressure suitable to effect condensation and separation from the vapors of constituents too high boiling vfor inclusion in the motor fuel product. A pressure equal to or lower than that of separator 4 may be employed, valve 26 in line 24 being provided for any desired reduction in pressure. The liquid condensate in fractionator 5 is collected in the bottom and may be withdrawn therefrom through line 21. Any desired proportion of the liquid condensate thus obtained may be recycled to the entrance of pipe coil 2 by means of line 2.8 which connects line 21'with line Ill.

The uncondense'd vapors pass overhead from fractionator 5 through line 29 to a cooler 30 in which condensation kof the motor-fuel constituents is effected. Cooling of the vapors may be assisted by passage thereof through heat exchanger 48 inv indirect heat exchange with fresh feed to the system. The resulting mixture oi liquids and gases passes from cooler 30 through line 3| to collector 6 in which separation of liquids and gases is effected. The gases may be withdrawn from collector 6 through line 32. The liquid condensate is withdrawn from collector 6 through line 33. A portion of the liquid condensate from collector 6 may be returned to fractionator 5 as reux through line 34 which is provided with a pump 35 and connects line 33 with the upper portion of fractionator 5. l

Instead of or in addition to the introduction to the system of a clean distillate `oil .as fresh feed through line l0 hydrocarbon oil of thisnature may be introduced into thel system through line 59 which is provided with a pump 50 and connects with absorber 5l wherein the hydrocarbon oil is passed in intimate contact with gases introduced into absorber 6| from collector through line `32.. The operation of absorber 6I is maintained to effect absorption by the hydrocarbon oil of the heavier constituents of they gases passing therethrough. The dry gases remaining are withdrawn from absorber 6| through line 62. The enriched hydrocarbon oil is withdrawn Afrom the lower portion of absorber 6I through line 63, passes through heat exchanger 48, vapor heat exchanger 64 and is combined with the cycle gas oil passing to coil 2a through line 28. By this means convertible constituents in the gases from collector 6 such as heavier normally gaseous hydrocarbons susceptible to conversion to liquids may be recovered and returned to the system. This operation is advantageous where it is desired to admix with the oil passing to the inlet ofl coil 2a convertible gaseous hydrocarbons to be converted to liquid products during the cracking treatment.

Gases suitable for such gas reversion treatment .also may be obtainedvfrom they stabilization treatment of the gasoline. The condensate passing through line 33 is transferred by means of pump 65 to gasoline stabilizer 66 in which conditions of temperature and rpressure are maintained to effect stripping from the condensate of gaseous hydrocarbons undesired in the gasoline product which is Withdrawn therefrom through line 61. Uncondensed gases are withdrawn overhead through line 68, are cooled in cooler 69 to effect condensation thereof, and the condensate is introduced into collector 10 in which any uncondensed gases are separated and withdrawn through line 1I. The liquefied normally gaseous hydrocarbons are withdrawn from collector 'l0 through line 12 provided with pump 13 and passed to admixture with the cycle gas oil passing through line 28 to the inlet of coil 2a. If desired a portion of the liquefied gases may be diverted from line 12 through line 14 for return to the upper portion of stabilizer 63 as reflux liquid. Gas reversion is particularly advantageous in connection with the operation of this invention in that it facilitates separation in separator 3 andin that the presence of recirculated gas in the clean oil section of coil 2a and in coil 2b materially assists in polymerizing unsaturated constituents into gasoline.

Instead of, or in addition to, the introduction to the system of a clean distillate oil as fresh feed through line I0 or line 59 hydrocarbon oil of this nature may be introduced into thesystem through line 36 which is provided with a pump 31 and connects with fractionator 5. The hydrocarbon oil thus introduced into fractionator 5 serves as cooling medium to assist fractionation therein and is stripped of any gasoline constituents contained therein. The remaining unvaporized portion, together with condensate from the vapors introduced into line 24, is withdrawn through line 21 as described and passed to the entrance: of pipe coil 2 through line 28.

Separator l! may be employed to effect the preliminary treatment of a heavy or residual oil introduced to the system. as fresh feedby removal therefrom of constituents suitable for recycling to the entrance of pipe coil 2 or suitable for inclusion in the motor fuel product.A Furthermo're, separator 4 may be employed to effect a cracking or a viscosity breaking of such heavy oil. I-Ieavy oil, such as heavy gas oil, crude voil or a reduced crude may be introduced into separator 4 through line 38 provided with a pump 39. This oil may be preheated suitably to eflect any desired cooling of the products of cracking in'separator 4. In separator 4 the heavy oil thus introduced is intimately admixed with the products of cracking introduced through line 2l to effect distillation and any desired cracking or viscosity breaking of .the heavy oil. The unvaporized residue from the heavy oil introduced through line 38 and residue from the cracked products introduced through line 2i are withdrawn through line 23. When it is desired to subject the residual oil thus collected in separator 4 to further cracking it may be introduced into section 2a of pipe coil 2 through line l2 or may be introduced into separator 3 through line i9. In this event the operating conditions of sepa.- rator 4 may be maintained to effect the inclusion of any desired proportion` of the heavy oil and cracked products in the residue thus collected. Line 40 connecting line 23 with line I9 is pro-- vided for the passage of any desired proportion of .this heavy oil to separator 3; Line 4I connecting line 23 with line I2 is provided to effect pas` sage of any desired proportion of the residual oil from-separator 4 into an intermediate point or points of. section 2a of the pipe coil.

In most cases it is desirable to carry onthe cracking reaction with respect to the residual constituents of the crude oil in a once-through manner and avoid recirculating residual products of cracking to the cracking zone. An advantageous operation in accordance with the invention is to introduce the topped or reduced crude into a primary dephlegmating or fractionating zone interposed between the zone of separation of cracked products, from line 2i, and the fractionator 5 in which the separated vapors from the cracked products are given a primary dephlegmation or fractionation and the bottoms from this primary fractionation are employed as the stock that is introduced either at I2 to the cracking coil 2a. or as the stock introduced at I9 into the separator 3.

To provide for this operation, separator 4 may 25V' be equipped with a trap-out tray 42, to provide a primary fractionating or dephlegmating zone 4a in the upper portion thereof, from which condensate and and unvaporized charge material from line 38 may be Withdrawn separately through line 43 which connects with line 4I, whereby this liquid may be introduced to the cracking coil at I 2. Branch line 44 connects lines 43 and 40 whereby this liquid may be introduced into separator 3 at I9. The vapors from this primary fractionating zone 4a pass to the fractionator 5, the clean condensate from which is cycled through line 28 to the cracking coil 2 as has been explained.

Although the separator 4 may be employed as a low pressure evaporator, with relatively small amounts of cracking being carried on therein, an advantageous operation, in accordance with the invention, is to maintain conditions of temperature and pressure adequate to carry on extensive cracking therein. In the latter operation, the cracking may, in accordance with the invention, be restricted with respect to the liquid components by withdrawing the liquid separatingout at such a rate as to prevent the accumulation of liquid in the separating chamber.

With the introduction of a heavy oil into separator 4 the low-boiling constituents thereof pass overhead through line 24 into fractionator 5 wherein they are separated in the manner described into a condensate suitable for charging stock and a vapor fraction containing motorfuel constituents. vided with suitable trays or bubble caps or other gas and liquid contact means for promoting the condensation, absorption, stripping and evaporation incidental to the desired fractionation.

In an example of the invention, clean condensate stock is subjected to cracking in the heating coil 2a at a temperature of 1000 F. Reduced crude preheated to a temperature of 650 F. is introduced into the intermediate separator 3. The liquid separating out in chamber 3 is rapidly withdrawn through line I6 and the separated ivapors, at a temperature of 800 F., pass to the cracking coil 2ar in which the vapors are subjected to cracking at a temperature of 950 F. Cracking is continued in the separator 4, which is maintained at 400 pounds pressure and at a temperature of 850 F., the residual constituents of cracking being Withdrawn at a rate adequate Fractionator 5 may be proto prevent separator. Y H f In another example of the invention clean distillate stockis subjected to cracking at a tem-` perature of 1000o F. in cracking coil 2a and reduced crude which has been preheated to a temperature of 750 F. is introduced through line I2 and the commingled products are subjected to cracking at a temperature of 900 F. in the latter portion of the coil 2a.. Vapors at a temperature of 825 F. pass from the intermediate separator 3 to the cracking coil 2b in which the vapors are subjected to cracking at a temperature' of 950 the accumulation'fof liquidfsin the F. The cracking is continued in the separator 4 y under 400 pounds pressure at a temperature of' 850 F., the residual products of cracking being withdrawn so as to prevent the accumulation of. liquid in the separator. The invention has been described with reference to a specic embodiment thereof, but it is to be understood that this is not limited by such specific reference but is capable of other embodi-vl ments which may be beyond the physical limitations of the apparatus illustrated.`

I claim: l v 1. The method of cracking hydrocarbon oil that comprises passing a stream of hydrocarbon oil under superatmospheric pressure throughprimary and secondary sections of an elongated heating zone of restricted cross section, applying heat to said primary vsection of the elongated heating zone to subject th'e stream of oil flowing therein to cracking temperaturev and eiect substantial cracking, introducing 4oil formed as hereinafter specied intofthe secondary section of the elongated heating zone so that the resultant mixture of said oil and the products from the' primary section of the elongated heating ,zone` constitutes the stream fiowing in the secondaryk section thereof, applying heat to'said secondary sectionA of the elongated heating zone tosubject the stream flowing therein to cracking'tempera-A ture and continue the cracking, delivering the resultant cracked products from the secondary section of the elongated heating zone to an enlarged separating zone maintained under super-- atmospheric pressure wherein separation of vapors from residue takes place, passing the separated vapors to a second elongated heating zone of restricted cross section wherein the vapors are heated and subjected to vapor phase cracking, directing the resultant cracked products into a second enlarged separating Zone wherein separation of vapors from residue takes place, passing separated vapors from7 the second enlarged separating Zone to a primary fractionating zone, withdrawing residue from the rst enlarged separating zone and subjecting it to flash'distillation under reduced pressureto produce a ashed condensate, introducing resultant ashed con-y densate into the primary fractionating zone wherein fractionation takes place to separate uncondensed vapors from a fraction comprising reiiuxcondensate and unvaporized constituents of the introduced iiashed condensate, conducting said fraction comprising reiiuX 'condensate and unvaporized constituents of the flashed condensate from the primary fractionating zone as the aforesaid oil introduced into the secondary section ofthe iirst elongated heating zone, submary section of the first elongated rheating Zonen.

2. The method of cracking hydrocarbon oil thatv comprises passingv a stream of hydrocarbon oi1 lunder superatmosphericpressure through primary and secon-daryf sections of `an elongated heating zone of restricted cross section, applying heat to said primary section of the elongated heating Zone to subject the stream of oil flowing therein to cracking temperature and effect substantial cracking, introducing oil formed as hereinafter specified into the secondary section of the lelongated heating zone so that the resultant mixture of said oil and the products from the primary section of the elongated heating zone constitutes the stream flowingin the secondary section thereof, applying heat to said secondary section of the elongated heating zone to subject the,v stream fiowing therein to cracking temperature and continue the cracking, delivering the resultant cracked products from the secondary section of the elongatedheating Zone to an enlarged separating Zone maintained under superatmospheric pressure wherein separation of vapors from residue takes place, passing the separated` vapors to a second elongated heatingzzone of restricted cross section wherein the vapors are heated and subjected to vapor phase cracking, directingthe resultant cracked products into a second enlarged separating zone wherein separation of vapors from residue takes place, passing separated vapors from the second enlarged separating Zone to a primary fractionating zone, withdrawing residuefrom the first enlarged separating zone and subjecting it to flash distillation under reduced pressure to produce a flashed condensate, introducing resultant flashed condensate and charging stock into the primary fractionating vzone wherein fractionation takes place to separate uncondensed vapors from a fraction comprising a mixture of reflux conden- -sate and unvaporized constitutents of the introduced flashed condensate and charging stock, conducting said mixture from the primary fractionating zone as the aforesaid oil introduced intothe secondary section of the elongated section of the heating Zone, subjecting separated vapors from the primary fractionating zone to further fractionation to separate a reux condensate from lighter products and cycling vsaid reflux condensate to the primary section of the first elongated heating zone.

3. The method of cracking hydrocarbon oil that comprises passing a stream of hydrocarbon oil under superatmospheric pressure through primary and secondary sections of an elongated heating zone of restricted cross section, applying heat to said primary section of the elongated heating Zone to subject the stream of oil flowing therein to cracking temperature and effect substantial cracking, introducing oil formed as hereinafter specified into the secondary sectionof the elongated heating Zone so that the resultant mixture of said oil and the products from the primary section of the elongated heating Zone constitutes the stream flowing in the secondary section thereof, applying heat to said secondary section of the elongated heating zone to subject the stream flowing therein to cracking temperature and continue the cracking, delivering the resultant cracked products from the secondary section of the elongated heating Zone to an enlarged separating zone wherein separation of vapors from residue takes place, passing the separated vapors to a second elongated heating zone of restricted cross section wherein the vapors are heated and subjected to vapor phase cracking,` directing the resultant cracked products into a second enlarged separating Zone wherein separation of vapors from residue takes place, passing separated vapors from the second enlarged separating Zone to a primary fractionating Zone, withdrawing residue from the first enlarged separating zone and passing it to a vacuum distilling zone wherein it is subjected to distillation under subatmospheric pressure to produce a vacuum distilled condensate, introducing resultant vacuum distilled condensate and charging stock comprising residual constituents ofA crude petroleum into theprimary fractionating Zone wherein fractionation takes place to separate uncondensed vapors from a fraction comprising a mixture of reflux condensate and unvaporized constituents of the introduced vacnum distilled condensate and charging stock, conducting said mixture from'the primary fractionating zone as the aforesaid oil introduced into the secondary section of the elongated section of the heating Zone, subjecting separated vapors from the primary fractionating zone to further fractionation to separate a reflux condensatel from lighter products and cycling said reflux condensate to the primary section of the first elongated heating zone.

, 4. The method of cracking hydrocarbon oil that comprises passing a stream of hydrocarbon oil under superatmospheric pressure through primary and secondary sections of an elongated heating Zone of restricted cross section, applying heat to said primary section of the elongated heating zone to subject the stream of oil flowing therein to cracking temperature and effect substantial cracking, introducing oil formed as hereinafter specified into the secondary section of the elongated heating zone so that the resultant mixtureof said oil and the products from the primary section of the elongated heating zone constitutes the stream owing in the secondary section thereof applying heat to said secondary section of the elongated heating zone to subject the stream flowing therein to cracking temperature and continue the cracking, delivering the resultant cracked products from the secondary section of the elongated heating zone to an enlarged separating zone maintained under superatmospheric pressure wherein separation of vapors from residue takes place, passing the separated vapors to a second elongated heating zone of restricted cross section wherein the vapors are heated and subjected to Vapor phase cracking, directing the resultant cracked products into a second enlarged separating Zone wherein separation of vapors from residue takes place, passing separated vapors from the second enlarged separating Zone to a primary fractionating zone, introduced charging stock comprising residual constituents of crude petroleum into said primary fractionating Zone wherein fractionation takes place to separate uncondensed vapors from a fraction comprising reflux condensate and unvaporized constituents of the introduced charging stock, conducting said fraction comprising reflux condensate and unvaporized constituents of the charging stock from the primary fractionating zone as the aforesaid oil introduced into the secondary section o-f the first elongated heating zone, subjecting separated vapors from the primary fractionating Zone to further fractionation to separate a reflux condensate from lighter products and cycling said reflux condensate to the primary section of the first elongated heating zone.

nsl

, 5. The method of cracking hydrocarbon oil that comprises passing a stream of hydrocarbon oil under superatmospheric pressure through pri'- mary and secondary sections of an elongated heating zone of restricted cross section, applying heat to said primary section of the elongated heating zone to subject the stream of oil owing thereiny to cracking temperature'and eiTect substantial cracking, introducing oil formed as hereinafter specied into the secondary section of the elongated heating zone so that the resultant mixture of said oil and the products from the primary section of the elongated heatingzone constitutes the stream flowing in the secondary section thereof, applying heat to said secondary section of the elongated heating Zone to subject the stream flowing therein to cracking temperature' and continue the cracking, delivering the resultant cracked products from the secondary section of the elongated heating zone to an enlarged separating zone maintained under superatmospheric pressure wherein separation of Vapors from residue takes place, passing the separated vapors to a second elongated heating zone of restricted cross section wherein the vvapors are heated and subjected to vapor phase cracking, directing the resultant cracked products into a second enlarged separating zone wherein separation of vapors from residue takes place,

passing separated vapors fromthesecond enlarged separating zone to a primary fractionating zone, introducing charging stock comprising residual constituents of crude petroleum into saidl primary fractionating zone'wherein fractionation takes place to separate uncony densed vapors from a fraction comprising reuX condensate and unvaporzed constituents of the introduced charging stock, conducting said fraction "comprising reflux condensate and unvaporized constituents of the charging stock from the primary fractionating zone as the aforesaid oil introduced into the secondary section of the first elongated heating zone, passing separated vapors from the primary fractionating Zone toa secondary fractionating zone wherein the vapors are fractionated to separate aref-lux condensate from vapors and gases, cycling said reux condensate to the primary section of the rst e1on' f gated heating zone, subjecting the separated Vapors and gases from the secondary fractionating Zone to further fractionation to form distillate and lighter and heavier fratctions comprising normally gaseous constituents and directing the heavier fraction comprising normally gaseous constituents to the primary section of thefirst elongated heating zone. t

` RICHABD F. TROW. 

